Spool valves control, i.e., switch, the direction of flow of a hydraulic fluid by moving a spool axially along a longitudinal axis within a bore of a valve housing between at least a first position and a second position. Movement of the spool opens and/or closes fluid communication between various ports defined by the valve housing to direct the hydraulic fluid along at least one of a first flow path and a second flow path.
The spool includes multiple land portions that each include a diameter substantially equal to a diameter of the bore within which the spool is disposed. The land portions are each configured for sealing against the bore. The various land portions define therebetween multiple fluid directing portions. The fluid directing portions are in fluid communication with the various ports defined by the valve housing, and are sealed from each other by the various land portions. The fluid directing portions cooperate with the bore to define fluid chambers, through which the hydraulic fluid flows from one port to another.
In operation, the hydraulic fluid flows from the various ports into the fluid chambers, and flows along an outer surface of the various fluid directing portions of the spool. Accordingly, the shape of the outer surface of the fluid directing portions of the spool directly affects the flow characteristics of the hydraulic fluid flowing through the fluid chambers.